A phase change material (PCM), which can be electrically switched between an insulative amorphous phase and a conductive crystalline phase, for an electronic memory application is used for a PRAM (phase change random-access memory) device (also known as an ovonic memory device or a PCRAM device). For typical phase change materials suitable for these applications, various elements of the VIB group (chalcogenide, for example, Te or Po) and the VP group (for example, Sb) in the periodic table are used in combination with one or more metal elements, such as In, Ge, Ga, Sn, or Ag. A particularly useful phase change material is a germanium (Ge)-antimony (Sb)-tellurium (Te) alloy (GST alloy). These materials can reversibly change their physical conditions depending on the heating/cooling rate, temperature, and time. Examples of other useful alloys include indium antimonite (InSb). The memory information in the PRAM device is stored with minimized loss due to the conduction characteristics of different physical phases or states.
Chemical mechanical polishing (CMP) is known as a process for polishing a metal-containing surface of a semiconductor substrate (for example, integrated circuit). The polishing composition used in CMP typically contains abrasive grains, an oxidizing agent, and a complexing agent to effectively polish the surface through etching.
The CMP can be performed to manufacture a memory device using a phase change material. However, unlike a conventional metal layer composed of a single component such as copper (Cu) or tungsten (W), the phase change material subject to polishing is prepared by mixing sulfur (S), cerium (Ce), germanium (Ge), antimony (Sb), tellurium (Te), silver (Ag), indium (In), tin (Sn), and gallium (Ga) at a specific ratio that allows reversible phase change between a crystal phase and an amorphous phase. For this reason, the physical properties of many phase change materials (for example, GST) differ from the physical properties of conventional metal layer materials, for example, are “softer” than other materials used in a PCM chip. Therefore, it is difficult to use the polishing composition for polishing present metal-containing surfaces to polish a phase change material.
Under such a situation, various studies have been conducted on polishing compositions suitable for polishing a polishing subject having a phase change alloy. For example, Patent Document 1 discloses a polishing composition for polishing a polishing subject having a phase change alloy and containing abrasive grains and a nitrogen compound. Further, Patent Document 2 discloses a polishing composition for polishing a polishing subject having a phase change alloy and containing abrasive grains and iron ions or an iron chelate complex. However, these inventions alone are not sufficient as a polishing composition for polishing a polishing subject having a phase change alloy. Thus, there is room for improvements.